The present invention relates primarily to a flow regulator for use in a parenteral solution administration set, and more particularly to a flow regulator which sustains fluid flow to the patient at a reduced rate after the level of fluid in the intravenous fluid (IV) container drops below a predetermined threshold, and to a flow regulator which provides accurate regulation of the total flow rate of the intravenous infusion. In one design, in addition to the above stated functions, total flow rate is adjustable and may be maintained very constant over the time of infusion, and complete filtration of the parenteral solution fluid is provided. In another design, the total flow rate is fixed at a maximum level, and minor adjustments to the flow rate are accomplished by changing the height of the IV container relative to the patient.
In my co-pending U.S. patent application, Ser. No. 702,068, filed July 2, 1976, and entitled "Automatic Intravenous Flow Regulator", I explained the desirability of maintaining the flow of parenteral solution for an extended period of time after the IV container becomes empty, and the problems which result when fluid flow ceases. Briefly stated, if the flow of parenteral solution ceases, even for a brief period of time, the intravenous infusion catheter often becomes clotted, necessitating an intravenous catheter or needle change, with the accompanying discomfort to the patient, incurred cost of materials, and loss of employee time.
In my aforementioned co-pending patent application, there is disclosed a mechanism which associates with an IV container, and which maintains fluid flow for a prolonged period of time even when the container is empty. This mechanism includes a reservoir chamber for receiving and storing parenteral solution from the IV container, and a valving arrangement for automatically decreasing the fluid flow rate to a lower secondary rate once the infusion bottle is empty and fluid level in the reservoir drops below a predetermined threshold level.
A main purpose of the present invention is to accomplish reduced fluid flow when the IV container becomes nearly empty, without the necessity for a special reservoir chamber and its associated valving.
Another main purpose of this present invention is to provide accurate flow rate regulation. Flow rate in most intravenous administration sets is regulated by roller clamps or other means of constricting the orifice of the IV infusing tubing to limit the flow of fluid. However, due to "creep" or "cold flow" of the plastic employed in the IV tubing, flow tends to decrease with time and often will decrease as much as 60% of the desired rate within one hour. Such inaccurate flow regulation necessitates frequent monitoring by hospital personnel to maintain the correct flow. This problem not only results in a waste of valuable medical personnel time but also increases the possibility that the intravenous infusion may be stopped prematurely. To solve this long-standing problem, recently many expensive electronic and magnetic monitoring and motorized pumping devices have become available. These devices, although solving to some extent the present problem, are expensive, cost much more than a simple infusion set, and require frequent nursing personnel visits to assure that the devices remain operational.